Substation telephone circuits



Jan. 31, 1928. 1,657,635

T. G. MARTIN SUBSTATION TELEPHONE CIRCUITS Original Filed March 15/1921 Q P QCR/ v l, a v (I J V j Q {.2 Q v -Im rsn 1:l1"v

TEUJTJT ENE FEE Patented Jan. 31, 1928.

UNITED STATES PATENT OFFICE.

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., F CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

SUBSTATION TELEPHONE CIRCUITS.

Application filed March 15, 1921, Serial No. 452,461. Renewed April 27, 1925. i

The present invention relates in general to substation telephone circuits, but more especially to substation telephone circuits for au tomatic telephone systems; and the object of a the invention is to provide a novel andimproved circuit arrangement for an automatic desk telephone.

A two wire calling device used in combination'with a standard Bell talking circuit,

In and the primary object in designing the cir cuitwas to so arrange the parts as to secure a minimum number of conductors in the cord connecting the telephone proper vith the bell box. In this respect the invention may be considered a further improvement on my pending application, Serial it l lilfiml, filed March 2, 1921, which in turn is an improvement on. the latent to l l illis, No. 1,313,570,

granted August 19, 1919. In my prior application referred to only tour conductors are required in the cord and the circuit is very satisfactory in every respect.

On further consideration of the matter it seemed desirable to reduce the number of M cord conductors to three, it this could be done in any way Without a sacrifice of elliciency in operating characteristics. The most obvious way to save another conductor is to bridge the ringer and condenser dist rectly across the line, as is done in party line systems, but previous experience has shown that to do this would. seriously impair the eliiciency oil the impulse transmitting circuit, or at least it would. do so it the ringer and w condenser were ltiridgcd across the line alone in the ordinary manner. I have found, however, that by arranging the circuit so that while impulses are being transmitted the two induction coil windings in series will be connectcd in parallel with the ringer, the ill effects previously caused by the bridged ringer and condenser are eliminated, and an int pulse tranr-m'iitting circuit is obtained which is not only perfectly satisfactory, but is ac i t-ually more eliicient under most conditions met in practice than is a simple series circuit without any bridges whatever.

Shuntcircuits are also provided for preventing noises in. the receiver while impulses are being transmitted, and for cutting out the transmitter at the same time, and it will be seen then that without sacrificing any valuable features found in prior circuits. I have produced a circuit for an automatic the operation thereof more in detail, referdesk telephone which requires only three conductors in the cord and which at the same time includes an impulse transmitting circuit of pronounced elliciency. In view of the latter feature it will be understood that the circuit may also be used to an advantage in a wall telephone.

Having set forth the object and scope of the invention in general terms, I will now explain the circuits and apparatus involved in once being had to the accompanying drawings, in which Fig. 1 is a wiring diagram of an automatic desk telephone and bell-box, Fig. 2 is a simplified circuit diagram, while Fig. 3 is a schematic diagram of the impulse transmitting circuit.

Referring first to Fig. 2, the talking circuit as before stated is of the well known Bell common battery type. -With the re ceiver removed from the switch-hook the 7" transmitter T and the winding 4 of the in-' duction coil are bridged across the two line conductors 2 and 3, while the receiver R in series with the winding 5 of the induction coil, and the condenser C is connected in so shunt of the transmitter. "The transmitter and receiver circuits are.bothnorinally open and are closed in the usual manner by the switch-hook H when the receiver is removed. Contact springs G and 7 are included in the 8 receiver circuit, while contact springs 8 and 9 are included in the transmitter bridge.

For receiving incoming signals the ringer M is provided, which is normally bridged across the line independent of control by the switch-hook. It will be observed that the ringer bridge includes a condenser, and that this condenser is the same one which is in cluded in the local circuit of the receiver, a common condenser being used for the ringer and receiver circuits. A little further consideration will show that when the contact springs '5 and '4' are closed by the removal of the receiver the secondary winding 5 of the induction coil, the receiver R, and the primary winding 4c of the induction coil, all in series, are connected in shunt of the ringer M. The ellect of this shunt circuit will be. considered more fully later on. k p 7 Associated with the lower side of the line is subscribers impulse sender, or calling device, which is indicated by, the reference character S. This sender may be of the type which is shown and described on pages 3-1 and $5 oi Automatic 'l elephony by tfhnith and Campbell, published by the MoClraw- Hill Book Company. It (IOIIIIHiSQS essentially a pair of impulse springs 15 and 16 which are controlled by a am (not shown) through the medium of a linger ,hold dial (not shown) and three shunt springs 12 13 and 11, together with suitable means for retaining; these springs in the position shown in the drawing when the calling device is not in use, and tor :ausine' all three springs to come into engagement with each other when the callin device dial is turned from its normal position. The impulse springs 15 and lt are cijinnectml in series with the lower line conductor 2 and their function is to prt'iduee momentary interruptions oi the line circnit tor the iiurpose 0t operating the central oll'iceswitches. The function of the shunt springs 12, 13 and 14; is to short circuit or shunt the transmitter T and the receiver 11 while the calling device is being operatedto transmitimpulses. To accomplish this spring 12 is connected to the junction of the receiver and transmitter. spring, 13 is connected tothe other side of the receiver, while spring 1-1: is connected to the other side ot the transmitter, and it will be evident that withthe springs connected in this manner, when the are brought into engagement, the receiver and transmitter will be short circuited as stated.

In Fig. 1 the circuits have been drawn out in detail, corresponding parts being indirated by the same reference numerals as in Fig. 2. The apparatus at the right oil the drawin comprising the transmitter 'l, the receirer R, the switch-hook H. and. the 'alling device S, constitutes the desk telephone proper; while the apparatus at the left or the drawing and comprising the ringer M, the condenser O, and the induction coil 1 separate from the telephone and in accordance with the usual practice is located in the bell box. The tcleplmne provided with a terminal strip l? in the base thereof. and the hell box is provided with a terminal strip P. The various circuits are completed by means of a cord which connects the two terminal strips which. it will be observed, comprises only three conductors. The line extending to the exchange is connected at the terminal strip P as illustrated in the drawing.

The operation of the substation circuit is as *l ollows: When the receiver is removedto initiate a call, the switch-hook contact s n'ings 7 and 9 comeinto engagement with contact springs (i and 8, respectively, whereby the transmitter T is bridged across the line in series with the primary winding of the induction coil, and the receiver R is connected in shunt of the transmitter in series with the condenser C and the secondary winding: of the induction coil. Res iionsire to the closure of the transmitter bridre current is supplied to the transmitter from a bridged battery at the ct-uitral oliice (not shown) over the following path duetor ll, winding l: oi" the induction coil 1, transmitter T, switch-lnliolt springs and ll and the impulse springs 15 and 1(3 to line conductor The bridge at the central ot- Iice, which includes the battery, may also in accordance with the usual practice inclndeithe controlling relay of an automatic swileln the circuit oi the controlling relay including. therelore, the trainauittcr l, at the lelephone. it Follows that ably manipulating the calling device dial the calling subscriber may produce a series ol interruptions in the circuit olithe controlling relay to bring about the operation oi the switch.

Considering a little more closely the opcrations which lltllit) place at the telephone durine' the transmission of a series at impult it will be noticed that as soon as the dial turned from its normal position the shunt springs are lUFiQLl together, and the substation loop is completed over a path which. may be traced from the line conductor 3 b v way at winding i of the induction coil 1, shunt springs 12, 71.3, and l-l. SNlttlldifmlt springs 8 and 9 and the impulse spr'u y 15 and 16 to the line conductor it will be seen 't'rom this that the VIH'lZIl'Jh-l resistance of the transmitter is excluded from the switch control, or impulse transmitting circuit. during the entire time that the railin; device is in operation, and is included again in the bridge across the line only when the callinr device. dial returns to its normal position. At the same time that the transmitter is short circuited the receiver ll is also short circuitcd by -n1ea1is ot the shunt springs 12 and 1 This latter operation takes care of the usual requirement of silent. operation: in other words. with the receiver short ('ll'ttlllt-ftl the subscriber not annoyed by hearing! the clicks in the receiver, caused by the iinm'ruptions in the line circuit. Another result accomplished by the short circuiting oil the receiver is the reduetion at the llllpt'tltllltjt. ot the shunt circuit. connected around the ringer M. With the receiver cut out this shunt circuit includes only the windings t and 5 oil the inductimi coil.

"to continue, the lirst operation at the calliue dcriee brings about the operation oli a first selector switch at the cxcluinoc. and succeeding operations at the t'illllllj f device will now result in the (uieration of addition al switches until the connection is finally crunpletctl to the line of the called subscriber. it being understood that all of the switches are provided with controilint: relay bridges which. with the exception of he line coir kill , wi thstand i bridge in the last switch, are successively closed the condenser bridge is short circuitcut of? from the line after their associated ed and the condenser will be discharged. At

switches are operated.

The connection having been completed, conversation may be held as desired, the talking circuits functioning the same as usual in such cases. The receiver is replaced at the end of the conversation, the transmitter and receiver circuits are broken at the switchhook contacts, and further flow of direct current through the substation from the exchange is prevented. As a result all of the switches used in the connection at the central oitice are released and restored to normal in the usual manner. The substation is now in condition to receive incoming signalling currents which may come in over the line conductors 2 and 3 and pass through the ringer M and condenser C, whereby the ringer is actuated to advise the subscriber that he is being called. It is noted that with the receiver on the hook contact springs ('3 and 7 are separated and the shunt circuit around the ringer M is broken.

The impulse transmitting circuit which,

as before stated, is exceedingly efficient and reliable is shown in schematic form in Fig. 3, which shows the condition of the circuit through the subs ation when the dial is away from its normal position, in other words, while in'ipulses are being transmitted. The essential elements are the impulse springs, the permanent bridge including the condenser and the ringer, and the shunt around the ringer which includes the windings d and 5 of the induction. coil. Since all the non-essential elements, such as the contact springs, etc, and the elements which are short circuited are omitted in the schematic drawing, the relation between the parts shown may be perceived at once. It will not be necessary to go into a minute consideration of the operation of the circuit from a strictly technical standpoint, as there are 2. large number of different line conditions which enter into a theoretical discussion of the electrical properties of the circuit and a thorough treatment of the subject would bc come exceedingly complicated. It may be stated, however, that a certain amount of capacity connected in shunt ot' the impulse springs is an advantage under a. great many line conditions, especially if there is a considerable amount ol loop resistance. Notg this, when the condenser and !',ill;'tt are pern'iancntly connected across the line in the usual manner without shunting the ringer, the condenser injuriously affects the impulses because of the exceedingly high impedance of the ringer which. is in series with it, as this causes the condenser to charge and discharge very slowly. For instance, it we consider Fig. 3 and assume that the induction coil windings 4 and 5 are omitted, when the calling device springs are each interruption of the circuit the line rclay ot the switch at the exchange, if it operates properly, should deenergize at once, but

with the calling device springs open the con denser bridge is left across the line, and the condenser is immediately charged in series with the line relay. Owing to the fact that this charging circuit also includes the high impedance ringer, the condenser will charge slowly and the resulting current flow will be prolonged appreciably, thereby causing the de-energization of the line .elay to be do layed. In other words, the effect of the condenser and ringer bridge is to make the line relay sluggish in lfiSPOIltllDg to. interruptions of the line circuit.

Let us consider now the circuit with the induction coil windings present, connected as shown in F 3. The benefit derived by having the induction coil windings connecfl ed in shunt of the ringer while impulses are being transmitted seems to be due tothe fact that the condenser is caused to charge and discharge very much more rapidly. The im pedance ot' the induction coil windings is almost negligible and it will be evident, therefore, that with the circuit of Fig. 3 the corn denser will charge and discharge much more rapidly, and the charging current through the line relay will not be prolonged as in the former instance where the induction coil windings were not connected in shunt of the ringer, with the result that the line relay is deenergized much more promptly when its circuit is interrupted.

While the explanation might perhaps be further amplified, it is believed that the foregoing will suffice to enable the invention to be understood and used by those skilled in the art. It will be seen that I have dovised an especially advantageous circuit. for an automatic desk telephone which includes an impulse transmitting circuit of high clii ciency and which in addition has the various parts so arranged that only three conductors are required for connecting the telephone itself with the bell-box. 7

Having described my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

lVhat I claim as my invention is:

1. In a substation telephone set, an induction coil, a. transmitter and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge of the line, a receiver, a circuit for said receiver including a permanent connection between it and the said transmitter, the .aid condenser, and the second winding of said induction coil, an impulse sender tor producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the

iii

said second bridge remaining closed mean while, and means for closing a low impedance shunt circuit around the said ringer while the said sender is being operated.

2. In a substation telephone set, an induction coil, a transmitter and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge ot the line. a receiver, a circuit for said receiver including the said transmitter, the said condenser, and the second winding oi said induction coil, said receiver circuit being normally open at a point between it and the iinluction coil winding. switch hook contacts 'l'or closing; said point in the receiver circuit, a impulse sender lor producing; interruptions inthe said first bridge to transmit in'ipulses' over the line to the exchange, the said SQLOlHl bridge remaining closed meanwhile, means for closing a low impedance shunt circuit around the said ringer while the said sender isbcing operated, and means for short-circuitlug the said transn'iittcr at the same time.

In a substation telephone set, an in duction coil, a transmitter and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge ot the line, a receiver, a circuittor said receivcr including a permanently closed conncction between the receiver and the said transmitter, the said condenser, and the second winding ot said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit lll'lPLllSGS over the line to the exchange, the said second lu'idgre remaining closed meanwhile, a shunt circuit around the said ringer including the two windings of said induction coil and the said receiver, and means for short cireuiting said receiver while the said sender is being operated.

l. In a substation telephone set, a line circuit, an induction coil, a transmitter and one winding of said coil in a normally open bridge of said line, contact springs for closine' said bridge, a ringer and a condenser in a permanently closed bridge oi said line, a shunt circuit for said transmitter including said condenser, a second winding oi said coil, and acreceiver, a second set at contact springs in the shunt circuit between the receiver and the said second coil winding, an impulse solider l'or prtulucin interruptions in the said lirst bridge to transmit impulses over the line to the exchange, and means for closing a low impedance shunt circuit around the said ringer while the said sender is being); operated.

5. In a substation telephone set, an induction coil, a transmitter and one winding of said induction coilio a normally open bridge of the line, a ringer and a condenser in a second bridge or the line, a receiver, a circuit for said receiver including the saidtransanalgesia nutter, the said condenser, and the second winding of said induction coil, said receiver circuitbeing normally open at a point between it and the said induction coil winding, switchhi'iolc contacts i'or closing said iii-st bridge and said receiver circuit, an impulse sender 'lor l'noducing interruptions in the said lirst ln'idgre to transmit inipulaes over the line to the exchange, the said second bridge remaining closed meanwhile. and means for closing a low impedance shunt circuit around the said ringer while the said sender is being operated.

(i. In a substation tclepl'ioue wt, a line cir cuit, an induction coil, a transmitter and one winding ot said coil in a normally open bridge of :-=aid line, contacts tor (5l()i-illll' i aid bridge, a ringer and condenser in a second bridge oi. said line. a receiver having: one terminal connected to said first bridge at a point between the raid lransu'litler and coil winding, a normal v open connection extending; from the other rerciver terminal to the second bridge at a point between the raid condenser and ringer, contacts for closing." said connection, a calling device l'or prmluc inc interruptions in said lirst bridge to transmit impulses over said line circuit, said lireond bridge being maintained clored, and con tacts actuated during the operation ol' said calling device :lor short circuiting said receiver.

7. in a substation telephone act. a line circuit, an induction coil, a transmitter and one winding o'l said coil in a. normally open bridge of said line, contacts for closing said bridge, a ringer and coiulcneer in a eecoud bridge vof said line, a receiver having one terminal connected to said lllst bridge at a point between the said trausmil'le and coil winding, a i'iormally open conlu-rtiou extend-- ing from the other receiver terminal to the second bridge at a point betweini the said condenser and ringer, contacts for cloning; said connection, a calling device tor producinn interruptions in said [irst ln'ide'e to transmit impulses over said line circuit, said second bridge being maintained clonal. a shunt spring connected lo one terminal of said tranen'iittcr, a s zccond shunt spring con-- nccted to the other terminal ol said trail miller and to one terminal of said receiver. a third shunt spring colniccted to the other terminal. of said receiver, and llhllllri l'or closing said shunt springs together when the calling, device is operiiited.

8. In a substation telephone set. a line circuit, an, induction coil, a trauainitler and one winding of said coil in a noru'lall open bridge of said line, iuritchlirmk contacts for closing said bridge, a calling device having interrupter springs for opening said bridge, a. condenser and ringer in a second bridge of said line, a receiver, a normally open receiver circuit including the said receiver,

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lllll said transmitter, said interrupter springs, said condenser, and the second Winding of said coil, the said receiver having one terminal directly connected to one terminal of said transmitter by a single continuous conductor, svvitchhoolr contacts for closing said receiver circuit, and shunt springs closed during the operation of said calling device,

for short circuiting said receiver.

9. In a substation telephone set, a line circuit, an induction coil, a transmitter and one Winding of said coil in a normally open bridge of said line, switchhook contacts for closing said bridge, a calling device having' interrupter springs for opening said bridge, a condenser and ringer in a second bridge or" said line, a receiver, a normally open receiver circuit including the said receiver, said transmitter, said interrupter springs, said condenser, and the second Wind ing of said coil, the said receiver having one terminal directly connected to one ter minal of said transmitter by a single continuous conductor, switchhoolr contacts for closing said receiver circuit, and shunt springs closed during the operation of said calling device for short circuiting said receiver and said transmitter.

10. In a telephone system including a substation provided With impulse sending contacts, a receiver and a transmitter for said substation, an induction coil having its one Winding in circuit with said impulse sending contacts and its other winding in shunt circuit of said contacts, said shunt circuit including a switchhook contact located in the portion of the shunt circuit extending directly from the other Winding, a relay bridged across the line limbs of said telephone system, and means :for operating said contacts to open the circuit of said first winding to cause current to be induced in aid first Winding by said shunt- Winding to efl'ect a positive snap action of said relay.

In Witness whereof, I hereunto subscribe niy nan'ie this 24th day 01' February, A. 1)., 1921.

'1 M'IBOT G. MARTIN. 

